Those sound good to me. But I'd appriciate a second opinion. ^_^
Another way to ask would be:
--nanji kara, nanji made-- (from what time to what time) if you want a more specific answer.

Taitei, nanji kara nanji made nemasu ka?

However... the 'sensei ga imasen' might be wrong. ^^; It really doesn't seem to imply that you lack someone to teach you Japanese... but sounds more general like "is no teacher." But... I could be off-base. ):

Kates wrote:However... the 'sensei ga imasen' might be wrong. ^^; It really doesn't seem to imply that you lack someone to teach you Japanese... but sounds more general like "is no teacher." But... I could be off-base. ):